1. Field of the Invention
This invention relates to a bar-code reader apparatus that reads bar codes, and more particularly to the control of the decode start timing of a bar code.
2. Description of the Related Art
With the recent remarkable spread of POS (Point Of Sale) system, bar codes are finding their way into more various applications. A bar code is a symbol constructed in such a manner that bars and spaces of different sizes are combined in parallel to form a single bar code character, and if necessary, a character group including check digits are added in parallel, and then, for example, particular predetermined patterns, such as start and stop characters, are attached before and after the bar code character.
For bar codes widely used for general consumer goods, JAN (Japan Article Number) are standardized in Japan. Another application of bar codes is a distribution material symbol. This symbol is added to the JAN code in the form of a distribution identification code of one or two digits.
Any of the above bar code symbols is called a one-dimensional bar code. The amount of information that those code systems can handle is several tens of bytes at most.
Recently, however, there have been strong demands for a bar code to have a larger amount of information. As if to respond to such demands, various symbol systems called two-dimensional bar codes have been announced.
Any of those symbol systems has the advantage of being able to code a remarkably large amount of information as compared with one-dimensional bar code systems. In one of two-dimensional systems, the amount of information is increased by stacking one-dimensional bar codes. The symbols in such a system are called stacked bar codes. This type of stacked bar codes includes a code system called PDF-417 and a code system called CODE 49.
One of such bar-code readers for reading two-dimensional bar codes is constructed of an image formation optical system composed of lighting, a lens, and a two-dimensional image sensor such as a CCD. When a bar code is read with such a bar-code reader, a two-dimensional bar code is placed in the imaging area of the two-dimensional sensor. As a result, the bar-code image is focused on the two-dimensional image sensor, and the image information is supplied to a decoder as an image signal. The decoder converts the black and white image information of the bars and spaces into numerical information, which is then supplied as the decode result to the outside circuitry.
One method of starting such a decoding action is to always repeat decoding regardless of whether a bar code is present or not. Another method is to start decoding only after the sensor or the operator has judged that the bar code is in the proper position and is ready to be imaged.
As noted above, when a two-dimensional bar code is read, the bar code is moved from the outside into the inside of the imaging area.
with a conventional method that always repeats decoding, the reading of a two-dimensional bar code is begun while the bar code is still moving to the proper position almost in the center of the imaging area. In such a state where the entire bar code cannot be imaged, a bar code without an error correction function cannot be read at all, although bar codes with an error correction function, such as PDF 417 and DATD CODE, can be read. Even bar codes with an error correction function require time for error correction, so that the decoding time is longer than when the entire bar code is imaged.
Further, with a method in which the sensor or the operator judges whether a bar code has stopped in the proper position, a sensor device is necessary or the operator is forced to do extra activities, which is undesirable and liable to cause errors.